Matrix pore structure in crystalline rocks and evidences...

www.helsinki.fi/yliopisto

Matrix pore structure in crystalline

rocks and evidences for diffusion

properties

Maikki Siitari-Kauppi

Laboratory of radiochemistry, Department of chemistry

1

Matrix diffusion workshop

13.9.2012 VTT


Matrix diffusion studies begun late 80’s at HYRL:

-radionuclides transport properties in flow and in

matrix

-radionuclides sorption on crushed rock material

-rock matrix characterisation on core scale;

porosity,pore structure, PMMA method

-natural analoque studies

13.9.2012


Content

Background

Definitions (porosity, pore structure, diffusivity)

Pore apertures /Anion exclusion

PMMA method

HTO and Cl-36 through diffusion

C-14 MMA out diffusion

13.9.2012 4

Radionuclide transport in

geosphere


Chemical diffusion in Geomaterials :

why it is difficult to predict?

Pore network of rocks are complex PHYSICS

Pore connectivity?

Pore apertures?

Pore tortuosity?

Porosity vs. Diffusion?

The scale problem

Solute - mineral interactions are complex CHEMISTRY

Geochemical interactions

Sorption

Effect of pH, ionic force,

dissolution/precipitation…

Reactive transport : pore

space change against time

GEOLOGY

PMMA

autoradiography

100-2000 cm3

PET

mercury

porosimetry,

CT tomography

1-10 cm3

water saturation

porosimetry

10-100 cm3

Scale

porosity increase

In situ

Eva-Lena Tullborg, Sven Åke Larson Porosity in crystalline rocks – A matter of

scale Engineering Geology 84 (2006) 75–83


rdft

eD dK

Effective diffusion / pore diffusion

connected / diffusion porosity


Diffusion of solute in water

(free diffusion) flux prop. to concentration gradient

Diffusion of solute in pore space

System of parallel tubes or plates :

effect of porosity

Real pore network :

porosity and geometry effects

C : concentration in porewater mol.l-1

the proportionality factor is which is called Effective Diffusion coefficient

x

CDJ wF

x

CDJ wP

x

CGDJ wPo

ew DGD

First Fick law for diffusion

13.9.2012 9

M Ben Clennell Tortuosity: a guide through the maze From Lovell M.A.

and Harvey P.K. 1997 Developments in Petrophysics Geological

Society Special Publication No 122 pp 299-344


Porosity in geomaterials

• PORES

- micropores < 2 nm

- mesopores 2 nm – 50 nm

- macropores > 50 nm

• FISSURES

- long and narrow

- intra- and intergranular

- open or filled

- up to micrometers

• GRAIN BOUNDARIES and FRACTURES

13.9.2012 11

Anion exclusion (after Mitchell, 1976 in Frick, 1993)

Simplified schematic representation of

the bonding and distribution of water

molecules and ions on silicate surfaces

of the pore space and the relative

viscosity of the aqueous phase in

narrow pores.

13.9.2012 12

Anion repulsion/exclusion (after Mitchell , 1796 in Frick, 1993)

Schematic distribution of ions

in the vicinity of the mineral

surfaces. Approximate data on

the extent (nm) of the diffusive

double layer are obtained using

Gouy-Chapman theory

(Morel,1983, p 404-407)

Electrostatic interactions

dominate in narrow pores.

Anions are representative only

to a limited extent of diffusion

behaviour.


What was studied?

rock porosity, porosity versus mineralogy, morphology of pore space pores / fissures / fractures - tortuosity / constrictivity / pore apertures

connectivity – accessable pore space adjacent to the water flowing fracture

structure and mineralogical heterogeneities

diffusive properties

What were the methods?

• PMMA autoradiographic method + (particle tracking TDD)

• Petrographic analyses, optical microscopy, electron microscopy, confocal laser

microscopy, energy dispersive X ray analyses

• CT microtomography

• Hg intrusion porosimetry, gas adsorption, water intrusion porosimetry

• He-gas method for permeability and diffusion

• through-diffusion/ in-diffusion with different probe molecules HTO, Cl, Na, Cs

in water phase


Autoradiography

10 cm

PMMA autoradiographic method

PMMA porosity patterns

in three granites

-different shades of grey on the

autoradiograph, represent different

porosities, the darker the shade the

higher the porosity

El Berrocal granite

Spain 0.3%

Grimsel

granodiorite

Switzerland 0.6%

Palmottu granite

Finland 0.7%

6 cm

pore apertures for

Grimsel granodiorite

pore apertures for

in situ PMMA

impregnated

Grimsel granodiorite

Pore apertures by Hg porosimetry

13.9.2012 17 Osasto / Henkilön nimi / Esityksen nimi

0

0.2

0.4

0.6

0.8

1

<0,1 0,1-0,5 0,5-1 1-1,5 1,5-2 >2

No

rma

lize

d f

req

uen

cy

Size bin (µm)

Microcrack aperture histogram

of “Kuru TK LAB 1”

Ouverture maximale

Ouverture minimale

MEB

0

0.5

1

<0,1 0,1-0,5 0,5-1 1-1,5 1,5-2 >2

No

rma

lize

d

freq

uen

cy

Size bin (µm)

Microcrack aperture histogram of

“Grimsel TK LAB”

Ouverture maximale

Ouverture minimale

MEB

Pore apertures from autoradiographs with

image analyses and by SEM


Muscovite

granite,

boulder from

Hämeenlinna

0.8%

3 cm

PMMA porosity patterns

In three granites

-different shades of grey on the

autoradiograph, represent

different porosities, the darker

the shade the higher the

porosity

R38 Olkiluoto

diatextic gneiss

0.2%

R38 Olkiluoto

pegmatite granite

0.4%

4 cm


Veigned gneiss

(Repro 323) 0.4%

4 cm


4 cm

Veigned gneiss

(Repro 323)

0.6%


4 cm

KR4 623 m 0.2%

13.9.2012 23

Through diffusion experiments


Out-Leaching Technique for Characterizing

Pore Fluids in Crystalline Rocks

Distilled water (about 55 ml) having no initial

chloride is placed into the reservoir (1 mm wide

water zone) and the water is chanced every 14

days . Concentration will increase as chloride from

rock pore space moves into the reservoir by

diffusion.

In situ water saturated rock core having an initial

chloride pore-water concentration of about 5 g/l

•about 30 cm in height

•4.2 cm in diameter

•porosity of 0.4 % >> total amount of chloride in

the matrix pore water about 10 mg

University of Helsinki, Radiochemistry Lab HYRL PRELIMINARY

RESULTS 3.2012

13.9.2012 25

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

0 50 100 150 200 250 300

A/A

o (

%)

time (days)

Olkiluoto tonalite 68.0m (through diffusion 277 d)

Cl-36

HTO

into tonalite matrix

25% of HTO

21% of Cl-36

out of tonalite matrix

4.5% of HTO

0.5% of Cl-36

De(HTO) = 1-3x10-13m2/s, α(HTO) = 0.3 %

De(Cl-36) =1-3x10-14m2/s, α(Cl-36)= 0.05 %

Da(HTO) = 0.5x1.5x10-10m2/s

Da(Cl-36) =2-4x10-11m2/s

13.9.2012 26

Comparison of the through-diffusion of HTO and chloride in two samples;

mica gneiss and basalt having porosities of 0.2 and 2%

Klobes P, Siitari-Kauppi M and Hellmuth K-H, Porosity characterisation

of selected nanoporous solids, STUK-YTO-TR 215


Outleaching of 14C- MMA

(Kivetty, unaltered porphyritic granodiorite)

-out diffusion occurs mainly along transgranular

fissures which form the main connective network

of porosity

Ki7_21

Da = 6.8x10

-11 m

2/s

sqrt(t)

0 1000 2000 3000 4000

A(t

)/A

0 V

/S

0.000

0.001

0.002

0.003

0.004

0.005

0.006

0.007

0.008

0.009

0.010

Experimental

Fit by short time -> Da

Theoretical maximum

Fit to longer times with same Da


Ki7_25

Da = 11x10

-11 m

2/s

sqrt(t)

0 1000 2000 3000 4000

A(t

)/A

0 V

/S

0.000

0.001

0.002

0.003

0.004

0.005

0.006

0.007

0.008

0.009

0.010

Experimental

Theoretical maximum


Fit to longer times with same Da

Outleaching of 14C- MMA

(Kivetty, slightly altered porphyritic granodiorite)

-diffusion occurs mainly along transgranular

fissures but porosity is increased due to alteration

/ intragranular porosity exists


Outleaching of 14C-MMA

(Kivetty, altered porphyritic granodiorite)

-due to strong alteration the complexity of

pore structure increases, intragranular porosity

has significant role in connected pore network

Ki7_122

Da = 1.8x10

-11 m

2/s

Da = 0.7x10

-11 m

2/s

sqrt(t)

0 1000 2000 3000 4000

A(t

)/A

0 V

/S

0.000

0.001

0.002

0.003

0.004

0.005

0.006

0.007

0.008

0.009

0.010

Experimental


Low Da from long time

High Da from short time

Theoretical maximum


He gas diffusion measurements (through diffusion) for

Finnish granites (data from 90’s)

gneiss

tonalite

granodiorite

pegmatite

www.helsinki.fi/yliopisto 31

Conclusions

Interconneted porosity was detected for the studied

rocks in core scale at lab by PMMA method, exceptions

were some gneisses from Olkiluoto

In situ porosity was found to be about 30-40% lower

than porosities measured at lab for Grimsel Granodiorite

Anion exclusion was pronounced for mica gneiss and

tonalite >> micro (<2 nm) and meso (<50 nm) pores

Anion exclusion was minor for fresh pegmatite

granite>>micro fissures (~≥ 1 µm)

He porosity was lower than tritium porosity for tonalite

and mica gneiss >> micro and meso pores


Thank you!


Matrix pore structure in crystalline rocks and evidences...

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